Chromium film for photomask and preparation method thereof

Abstract

The invention relates to a chromium film for a photomask and a preparation method thereof. The preparation method comprises the following steps: pretreating a substrate; depositing a transition layer on the pretreated substrate; performing oxygen-containing plasma interface activation on the transition layer; depositing a chromium main functional layer on the activated transition layer at low temperature and regulating stress to obtain a chromium film; and performing post-treatment to stabilize the structure and stress of the chromium film. The chromium film comprises a substrate which is a supporting carrier of the chromium film; the chromium main functional layer is a carrier for photoetching of the photomask, and the chromium main functional layer is arranged on the substrate; and the transition layer is configured to realize high bonding and stress buffering of the substrate and the chromium main functional layer, and the transition layer is arranged between the substrate and the chromium main functional layer. According to the invention, the stress of the film layer is fundamentally reduced, ultrahigh binding force is realized at ultralow temperature, and the pattern precision and uniformity are synchronously improved.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing technology, and to a chromium film for photomasks and a method for preparing the same, particularly to a low-stress chromium film for photomasks and a method for preparing the same. Background Technology

[0002] In the semiconductor manufacturing field, deep ultraviolet (DUV) lithography (such as ArF 193nm and KrF 248nm lithography) is the core process of ultra-large-scale integrated circuit manufacturing. As a key precision template in the lithography process, the quality of the light-shielding chromium film of the binary photomask directly determines the linewidth uniformity, edge roughness and positioning accuracy of the lithographic pattern, which has a decisive impact on the yield and performance of the chip manufacturing process.

[0003] In the fabrication of binary photomasks, the chromium film used as the light-shielding layer suffers from the following specific defects that urgently need to be addressed: 1) Local pattern distortion: Due to the high residual compressive stress (typically -400 MPa to -600 MPa) within the chromium film, this stress is unevenly released after patterning, leading to nanoscale local micro-distortion in the lithographic pattern, directly affecting the fidelity and overlay accuracy of the lithographic imaging; 2) Poor linewidth uniformity: The aforementioned uneven stress distribution and insufficient adhesion between the film layer and the quartz substrate can cause unpredictable micro-changes in the pattern linewidth during multiple cleaning and laser repair processes, causing the linewidth uniformity (CDU) of the entire mask to exceed the stringent specifications of advanced processes (such as <5nm nodes); 3) Process window conflicts: Increasing the deposition temperature to improve adhesion will exacerbate stress; while slowing down the deposition rate or reducing power to reduce stress will sacrifice production efficiency and film density. Traditional processes struggle to achieve a balance between "high adhesion, low stress, and high throughput." Summary of the Invention

[0004] This invention provides a chromium film for photomasks and its preparation method, specifically a low-stress chromium film for photomasks and its preparation method, which fundamentally reduces film stress and stably controls the intrinsic stress of the chromium film at a low level (target range of -100 MPa to +50 MPa), eliminating the main cause of local pattern distortion from the source, achieving ultra-high bonding force at ultra-low temperature, and simultaneously improving pattern accuracy and uniformity.

[0005] The first aspect of this invention provides a method for preparing a chromium film for a photomask, comprising: Pre-treatment of the substrate; A transition layer is deposited on the pretreated substrate; The transition layer is activated by an oxygen-containing plasma interface; A chromium main functional layer is deposited at low temperature on the activated transition layer, and stress is controlled to obtain a chromium film; and Post-processing is performed to stabilize the chromium film structure and stress.

[0006] Furthermore, the substrate is a quartz substrate or synthetic quartz glass.

[0007] Furthermore, the pretreatment includes ultraviolet ozone cleaning, wherein the ultraviolet wavelength is 185nm / 254nm and the irradiation time is 10~20 min.

[0008] Furthermore, the pretreatment also includes low-power plasma cleaning, wherein the plasma is an inert gas with a power ≤80W, a pressure of 0.3~0.5Pa, and a cleaning time of 100~150s.

[0009] Furthermore, the transition layer is a CrON gradient transition layer; and / or Depositing a transition layer on the pretreated substrate includes: O2 and N2 are introduced, with the total flow rate controlled at 30~50 sccm and the working pressure at 0.2~0.4 Pa. A Cr target is used, the sputtering power is 1.5~2.5 kW, and dynamic gas flow control is adopted to deposit a transition layer with a thickness of 5~8 nm within 60~70 seconds. The O2 to N2 flow ratio gradually changes from the initial (8~9):(1~2) to the final (1~2):(8~9).

[0010] Furthermore, the transition layer is a CrON gradient transition layer whose composition changes continuously from oxygen-rich to nitrogen-rich on the side in contact with the substrate and from nitrogen-rich on the side in contact with the chromium main functional layer in the thickness direction.

[0011] Further, the oxygen-containing plasma interface activation of the transition layer includes: Introduce a mixture of Ar / N2 / O2 gas; and Plasma treatment was performed under conditions of 0.3~0.5 Pa and 55~60 W. Furthermore, Ar / N 22 / O 22 The volume ratio is (85~90):(9~13):(1~2), and the plasma treatment time is 40~50 seconds.

[0012] Furthermore, low-temperature deposition of a chromium main functional layer and stress modulation on the activated transition layer include: A chromium master functional layer was deposited at low temperature using unbalanced magnetron sputtering technology. During the low-temperature deposition of the chromium master functional layer, the target power was 2.0–3.0 kW, and the substrate temperature was kept constant at 75–80 °C. A DC bias voltage of -50 to -60V is applied to the substrate to adjust the chromium film stress in real time; and / or The thickness of the chromium film is 80~90nm.

[0013] Further, the post-processing includes: The chromium film was subjected to low-temperature annealing under vacuum; wherein the vacuum degree was ≤1×10⁻⁶. -3 Pa, in the low-temperature annealing treatment, the annealing temperature is 150~170℃ and the annealing time is 20~30 min.

[0014] A second aspect of the present invention provides a chromium film, characterized in that it comprises: The substrate serves as a support for the chromium film. A chromium main functional layer, which serves as a carrier for photomasks to perform photolithography, is disposed on the substrate; and A transition layer, configured to achieve high bonding and stress buffering between the substrate and the chromium main functional layer, is disposed between the substrate and the chromium main functional layer; and / or The transition layer is a CrON gradient transition layer.

[0015] The principle and synergistic relationship of the chromium film preparation method of the present invention are as follows: 1. Gradient transition layer design: The CrON gradient transition layer is the core of achieving high bonding strength at low temperatures. Its composition gradually changes from SiO2 (oxygen-rich) at the bottom layer near the substrate to Cr layer (nitrogen-rich) at the surface, achieving perfect bridging in chemical bonds (Cr-O, Cr-N) and thermal expansion coefficients, thus forming strong interfacial bonding at low temperatures; 2) The special role of oxygen-containing plasma activation: Conventional Ar / N2 plasma is difficult to fully activate the CrON surface layer. This invention introduces trace amounts of O2, whose active oxygen species can preferentially combine with the dangling bonds on the transition layer surface to form an ultrathin, stable "atomic-level adhesive layer" rich in active sites, which lays the foundation for the subsequent epitaxial growth of Cr atoms. This is the key to achieving a "chemical bonding-dominated" interface. 3) Unbalanced magnetron sputtering and bias stress control: Unbalanced magnetron sputtering can generate high-density, low-temperature plasma. By precisely controlling the DC bias applied to the substrate, the ion energy bombarding the substrate can be adjusted. Lower energies (e.g., -30V) are beneficial for reducing compressive stress in the film layer and may even induce micro-tensile stress, thereby directly "sculpting" the desired low-stress film structure during the deposition process.

[0016] This invention primarily serves: Fabrication of deep ultraviolet (DUV) lithography, such as ArF (193nm) and KrF (248nm) lithography, using chromium binary photomasks; and Other high-precision photomasks or templates with extreme requirements for graphic linewidth uniformity (CD Uniformity), edge roughness (LWR), and positioning accuracy.

[0017] The present invention has at least the following beneficial effects: 1) The chromium film preparation method of the present invention can precisely control the chromium film stress from about -500 MPa in the traditional method to -50 MPa to +35 MPa. 1) Within the MPa range, pattern distortion caused by film stress is almost eliminated; 2) On a 100nm linewidth pattern, the mask prepared by this method can achieve a linewidth uniformity (CDU, 3σ) of ≤2.1nm, and the local pattern distortion value is reduced by more than 60%, meeting the requirements of the most advanced photolithography method; 3) This invention ensures that at extremely low method temperatures (≤80℃), the critical load (Lc) of the bonding force between the chromium film and the quartz substrate can still exceed 40N, and has passed more than 200 semiconductor standard cleaning process tests without any edge peeling, meeting the most stringent cleaning and service life requirements; 4) This invention decouples the two usually contradictory indicators of "bonding force" and "stress", and through the synergistic effect of low stress and high bonding force, improves the linewidth uniformity (CDU) of the mask pattern to a higher level, for example, improving the 3σ value from the conventional >4.0nm to <2.5nm, providing an independent and broad adjustment space for method optimization, and greatly improving production yield and repeatability. Attached Figure Description

[0018] To further illustrate the above and other advantages and features of the various embodiments of the present invention, a more specific description of the embodiments of the invention will be presented with reference to the accompanying drawings. It is to be understood that these drawings depict only typical embodiments of the invention and are therefore not intended to limit its scope. In the drawings, identical or corresponding parts will be indicated by identical or similar reference numerals for clarity.

[0019] Figure 1 A flowchart of a method for preparing a chromium film for a photomask is shown in some embodiments of the present invention; Figure 2 Schematic diagrams of chromium film structures in some embodiments of the present invention are shown; Figure label: 1-Quartz substrate, 2-CrON gradient transition layer, 3-Chromium main functional layer. Detailed Implementation

[0020] It should be noted that the components in the accompanying drawings may be shown exaggerated for illustrative purposes and may not be to scale.

[0021] In this invention, the various embodiments are merely intended to illustrate the solutions of the invention and should not be construed as limiting.

[0022] In this invention, unless otherwise specified, the quantifiers “a” and “one” do not exclude scenarios involving multiple elements.

[0023] It should also be noted that, in the embodiments of the present invention, only a portion of the parts or components may be shown for clarity and simplicity. However, those skilled in the art will understand that, under the teachings of the present invention, the required parts or components can be added as needed for specific scenarios.

[0024] It should also be noted that within the scope of this invention, the terms "same", "equal", and "equal to" do not mean that the two values ​​are absolutely equal, but allow for a certain reasonable error. In other words, the terms also cover "substantially the same", "substantially equal", and "substantially equal to".

[0025] It should also be noted that in the description of this invention, the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not explicitly or implicitly suggest that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0026] Furthermore, the embodiments of the present invention describe the method steps in a specific order; however, this is only for the convenience of distinguishing each step, and is not intended to limit the order of the steps. In different embodiments of the present invention, the order of the steps can be adjusted according to the method.

[0027] The following embodiments provide a method for preparing a chromium film for a photomask. Figure 1 A flowchart of the chromium film preparation method is shown, including: The quartz substrate 1 is pretreated, including ultraviolet ozone cleaning. In the ultraviolet ozone cleaning, the ultraviolet wavelength is 185nm / 254nm and the irradiation time is 10~20 min. After ultraviolet ozone cleaning, low-power plasma cleaning is performed. In the low-power plasma cleaning, the plasma is an inert gas with a power ≤80W, a pressure of 0.3~0.5Pa, and a cleaning time of 100~150s. A transition layer (CrON gradient transition layer 2, whose composition changes continuously from oxygen-rich to nitrogen-rich) is deposited on the pretreated quartz substrate 1: O2 and N2 are introduced and dynamic gas flow control is adopted to deposit a transition layer with a thickness of 5-8 nm within 60-70 seconds, wherein the O2 to N2 flow ratio gradually changes from the initial (8-9):(1-2) to the final (1-2):(8-9); Oxygen-containing plasma interface activation of the transition layer: Ar / N2 / O2 mixed gas is introduced; and plasma treatment is carried out under the conditions of 0.3~0.5 Pa and 55~60 W; the volume ratio of Ar / N2 / O2 is (85~90):(9~13):(1~2), and the plasma treatment time is 40~50 seconds; A chromium main functional layer 3 was deposited at low temperature on the activated transition layer, and stress was controlled to obtain a chromium film. The chromium main functional layer 3 was deposited at low temperature using unbalanced magnetron sputtering technology. During the low-temperature deposition of the chromium main functional layer 3, the target power was 2.0~3.0kW, and the substrate temperature was kept constant at 75~80℃. A DC bias voltage of -50~-60V was applied to the quartz substrate 1 to control the chromium film stress in real time. The thickness of the chromium film was 80~90nm. Post-treatment is performed to stabilize the chromium film structure and stress: the chromium film is subjected to low-temperature annealing in a vacuum environment; wherein the vacuum degree is ≤1×10 -3 Pa, in the low-temperature annealing treatment, the annealing temperature is 150~170℃ and the annealing time is 20~30 min.

[0028] The following embodiments also provide a chromium film, Figure 2 A schematic diagram of the chromium film structure is shown, including: Quartz substrate 1 serves as a support carrier for the chromium film and as the bottom substrate; The chromium main functional layer 3, which serves as the carrier for photomask lithography, is disposed on the quartz substrate 1; and The CrON gradient transition layer 2 is configured to achieve high bonding and stress buffering between the quartz substrate 1 and the chromium main functional layer 3. The CrON gradient transition layer 2 is located between the quartz substrate 1 and the chromium main functional layer 3. Its composition gradually changes from an oxygen-rich state at the bottom (near the quartz substrate 1) to a nitrogen-rich state at the top (near the chromium main functional layer 3). It is the key to achieving high bonding and stress buffering at low temperatures. The chromium main functional layer 3 achieves low stress and high bonding through the CrON gradient transition layer 2 below.

[0029] Example 1 – Fabrication of a binary chromium mask for 65nm node ArF lithography 1. Pretreatment: After UV / O3 cleaning, the quartz substrate 1 is cleaned with 80W Ar plasma at 0.4 Pa for 150 seconds.

[0030] 2. Deposition of CrON gradient transition layer 2: A 5 nm thick gradient CrON gradient transition layer 2 was deposited within 60 seconds using dynamic gas flow control (the O2 to N2 flow ratio gradually changed from the initial 8:2 to the final 1:9).

[0031] 3. Interface activation: A mixed gas of Ar:N2:O2 = 85:13:2 is introduced, and plasma treatment is performed for 45 seconds under the conditions of 0.5 Pa and 55 W.

[0032] 4. Deposit Cr main layer and control stress: Unbalanced magnetron sputtering was used with a target power of 3.0 kW, a constant substrate temperature of 75℃, and a -50V DC bias voltage to deposit an 80nm thick chromium film.

[0033] 5. Annealing: Anneal at 150°C in vacuum for 20 minutes.

[0034] Effect verification: Membrane stress: +35 MPa (micro-tension stress) as measured by laser curvature method.

[0035] Bonding force: The critical load (Lc) for the scratch test is 42.5 N.

[0036] Image accuracy: In complex image regions, CDU(3σ) is 2.05 nm, and local image distortion is reduced by 65% ​​compared to the control sample.

[0037] While some embodiments of the present invention have been described in this application, those skilled in the art will understand that these embodiments are merely illustrative. Numerous variations, alternatives, and improvements will arise in those skilled in the art under the teachings of this invention without departing from its scope. The appended claims are intended to define the scope of the invention and thereby cover methods and structures within the scope of the claims themselves and their equivalents.

Claims

1. A method for preparing a chromium film for a photomask, characterized in that, include: Deposit a transition layer on the substrate; The transition layer is activated by an oxygen-containing plasma interface; A chromium main functional layer is deposited at low temperature on the activated transition layer and the stress is controlled to obtain a chromium film. as well as Post-processing is performed to stabilize the chromium film structure and stress.

2. The method for preparing a chromium film for a photomask according to claim 1, characterized in that, The substrate is a quartz substrate or synthetic quartz glass.

3. The method for preparing a chromium film for a photomask according to claim 1, characterized in that, Also includes: Before depositing the transition layer, the substrate is pretreated, including ultraviolet ozone cleaning, in which the ultraviolet wavelength is 185nm / 254nm and the irradiation time is 10~20 min.

4. The method for preparing a chromium film for a photomask according to claim 3, characterized in that, The pretreatment also includes low-power plasma cleaning, in which the plasma is an inert gas with a power ≤80W, a pressure of 0.3~0.5Pa, and a cleaning time of 100~150s.

5. The method for preparing a chromium film for a photomask according to claim 1, characterized in that, The transition layer is a CrON gradient transition layer; and / or Depositing a transition layer on the substrate includes: O2 and N2 are introduced, with the total flow rate controlled at 30~50 sccm and the working pressure at 0.2~0.4 Pa. A Cr target is used, the sputtering power is 1.5~2.5 kW, and dynamic gas flow control is adopted to deposit a transition layer with a thickness of 5~8 nm within 60~70 seconds. The O2 to N2 flow ratio gradually changes from the initial (8~9):(1~2) to the final (1~2):(8~9).

6. The method for preparing a chromium film for a photomask according to claim 1, characterized in that, Oxygen-containing plasma interface activation of the transition layer includes: Introduce a mixture of Ar / N2 / O2 gas; and Plasma treatment was performed under conditions of 0.3~0.5 Pa and 55~60 W.

7. The method for preparing a chromium film for a photomask according to claim 6, characterized in that, The volume ratio of Ar / N2 / O2 is (85~90):(9~13):(1~2), and the plasma treatment time is 40~50 seconds.

8. The method for preparing a chromium film for a photomask according to claim 1, characterized in that, Low-temperature deposition of a chromium main functional layer on the activated transition layer and stress regulation include: A chromium master functional layer was deposited at low temperature using unbalanced magnetron sputtering technology. During the low-temperature deposition of the chromium master functional layer, the target power was 2.0–3.0 kW, and the substrate temperature was kept constant at 75–80 °C. A DC bias voltage of -50 to -60V is applied to the substrate to adjust the chromium film stress in real time; and / or The thickness of the chromium film is 80~90nm.

9. The method for preparing a chromium film for a photomask according to claim 1, characterized in that, The post-processing includes: The chromium film was subjected to low-temperature annealing under vacuum; wherein the vacuum degree was ≤1×10⁻⁶. -3 Pa, in the low-temperature annealing treatment, the annealing temperature is 150~170℃ and the annealing time is 20~30 min.

10. A chromium film, characterized in that, include: The substrate serves as a support for the chromium film. A chromium main functional layer, which serves as a carrier for photomasks to perform photolithography, is disposed on the substrate; as well as A transition layer, configured to achieve high bonding and stress buffering between the substrate and the chromium main functional layer, is disposed between the substrate and the chromium main functional layer; and / or The transition layer is a CrON gradient transition layer.

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